Method and apparatus for synchronization of base stations in a broadband wireless access system

ABSTRACT

Synchronization between base stations in a broadband wireless access system is achieved using interfering base stations. Interfering base stations are first identified for a base station of interest (BSOI). One of the interfering base stations is then selected to be a master base station for the BSOI. The BSOI may then establish and maintain synchronization with the master base station.

CROSS REFERENCE TO RELATE APPLICATIONS

This application claims benefit under USC 120 or 365(c) toPCT/RU2006/000101.

TECHNICAL FIELD

The invention relates generally to wireless communications and, moreparticularly, to broadband wireless networking.

BACKGROUND OF THE INVENTION

Broadband wireless access (BWA) systems are currently in developmentthat will provide high speed wireless network services over relativelylarge regions. One such technology is embodied in the IEEE 802.16wireless networking standard (IEEE Std 802.16-2004). Typically, suchsystems will utilize a number of distributed base stations to provideaccess services for users over an extended area. Each base station willprovide services for subscriber stations within a corresponding coveragearea or cell. Time division duplexing (TDD) is currently a preferredtechnique for managing communication between a base station and asubscriber station within a cell of a BWA system. That is, the basestation and the subscriber station will transmit signals to one anotherusing the same frequency, but the base station will transmit at adifferent time than the subscriber station. TDD has certain advantagesover frequency division duplexing (FDD), where the base stationtransmits at a different frequency from the subscriber station.

One communication technique that has become a popular choice for use inbroadband systems is orthogonal frequency division multiplexing(OFDM)/orthogonal frequency division multiple access (OFDMA). OFDM usesa plurality of relatively narrowband subcarriers to transmit datathrough a channel. Each subcarrier may be separately modulated with acorresponding data symbol within the transmitter. An “OFDM symbol” isthen transmitted that includes all of the subcarriers and theircorresponding symbols. OFDMA is a technique that may be used to providemultiple access in an OFDM system. In OFDMA, different subgroups ofsubcarriers within an OFDM symbol may be allocated to different users inthe system. It has been shown that maximum spectral efficiency may beachieved in an OFDMA system when each of the cells in the system utilizethe same frequency (i.e., frequency reuse 1). When TDD is being used insuch a scenario, interference between base stations may occur if onebase station is transmitting while another base station is receiving.Thus, if a portion of an uplink subframe in one cell occurs at the sametime as a portion of a downlink subframe in an adjacent cell (and viceversa), then communication within both cells may be compromised. Toprevent this from occurring, the base stations within a network may besynchronized so that uplink and downlink operations do not overlap.

It has been proposed that GPS receiver technology be provided withineach of the base stations within a BWA system for use in providingsynchronization between the base stations (see, e.g., IEEE Std802.16-2004). While GPS receivers are capable of providing accuratesynchronization, there are situations where their use may be limited. Ifit is desired to locate a base station within a building, for example,the GPS receiver may not be able to acquire an adequate number ofsatellite signals to generate accurate time information for use insynchronization. In addition, the inclusion of a GPS receiver in a basestation may add significant cost to the base station. In some BWA systemimplementations, for example, the cell size may be relatively small(e.g., 0.3-1 km), thus requiring a large number of pico-base stations tocover a given area. If base stations are expensive, the cost ofimplementing such a system may be prohibitive. If base stations areavailable that do not include GPS receivers, then system implementationcosts may be reduced significantly. For each of the above reasons, itmay be desirable to develop alternative techniques for synchronizing thebase stations of a BWA system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example broadband wireless access(BWA) system in accordance with an embodiment of the present invention;

FIG. 2 is a timing diagram illustrating interference between basestations in an OFDMA-based TDD BWA network environment;

FIG. 3 is a flowchart illustrating an example procedure for initiatingand maintaining synchronization between a base station of interest(BSOI) and other base stations in a system in accordance with anembodiment of the present invention;

FIG. 4 is a diagram illustrating an example base station synchronizationhierarchy that may exist within a BWA system in accordance with anembodiment of the present invention;

FIG. 5 is a flowchart illustrating an example method that may be used bya BSOT during a synchronization discovery phase in accordance with anembodiment of the present invention;

FIG. 6 is a flowchart illustrating an example method for use by networkcontrol functionality in a BWA system when a BSOI requests theassignment of a master base station for synchronization purposes inaccordance with an embodiment of the present invention;

FIG. 7 is a flowchart illustrating an example method for use by a BSOIto initially synchronize to a master base station and to periodicallycorrect this synchronization in accordance with an embodiment of thepresent invention;

FIG. 8 is a timing diagram illustrating example communication activitywithin a sync group of a BWA system in accordance with an embodiment ofthe present invention; and

FIG. 9 is a block diagram illustrating an example BSC architecture 180in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein in connection with one embodiment may beimplemented within other embodiments without departing from the spiritand scope of the invention. In addition, it is to be understood that thelocation or arrangement of individual elements within each disclosedembodiment may be modified without departing from the spirit and scopeof the invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to which the claims are entitled. Inthe drawings, like numerals refer to the same or similar functionalitythroughout the several views.

FIG. 1 is a diagram illustrating an example broadband wireless access(BWA) system 10 in accordance with an embodiment of the presentinvention. As illustrated, the BWA system 10 may include: a plurality ofbase stations 12, 14, 16, 18, 20, 22; an IP network 24 interconnectingthe base stations 12, 14, 16, 18, 20, 22; and a base station controller(BSC) 26. The base stations 12, 14, 16, 18, 20, 22 are each operativefor providing wireless access services for subscriber stations (notshown) within a corresponding coverage region or cell. The IP network 24allows the base stations 12, 14, 16, 18, 20, 22 to communicate with oneanother, with the BSC 26, and possibly with one or more other networksand/or entities (e.g., the Internet, a public switched telephone network(PSTN), etc.). The IP network 24 may be a wired network, a wirelessnetwork, or a hybrid wired/wireless network. The BSC 26 controls atleast some of the operational features of the base stations of the BWAsystem 10. The BSC 26 may be implemented within a separate controlserver within the system 10, within one of the base stations, or in someother network location. The base stations 12, 14, 16, 18, 20, 22 may, invarious embodiments, communicate with the BSC 26 using wired, wireless,or hybrid wired/wireless links.

In at least one implementation, the base stations 12, 14, 16, 18, 20, 22utilize OFDMA techniques to communicate with subscriber stations incorresponding cells. Transmissions from a base station to a subscriberstation are referred to as downlink transmissions and transmissions froma subscriber station to a base station are referred to as uplinktransmissions. In some embodiments, wireless communication within a cellis performed in consecutive frames. Each frame may be divided into adownlink subframe during which the base station transmits to thesubscriber stations and an uplink subframe during which the subscriberstations transmit to the base station. Because the downlink subframe andthe uplink subframe occur at different times, this is an example of TDDoperation.

In one operational scenario, the base stations 12, 14, 16, 18, 20, 22within the BWA network 10 may each be operated in the same frequencychannel. This raises the possibility that wireless transmissions withinone cell may cause interference within another nearby cell, therebyreducing communication quality within the other cell. For example, if afirst base station within a first cell is transmitting while a secondbase station within a neighboring second cell is receiving, thetransmitted signal from the first base station may make it difficult orimpossible for the second base station to accurately receive signalstransmitted to it by subscribers within the second cell. FIG. 2 is atiming diagram illustrating such an occurrence in an OFDMA-basedwireless network environment. As shown, a cell associated with a firstbase station (BS1) utilizes a first frame 30 to communicate withcorresponding subscriber stations and a cell associated with a second,neighboring base station (BS2) utilizes a second frame 32 to communicatewith its subscriber stations. Although not shown, such frames willrepeat over time within each cell. The first frame 30 includes adownlink subframe 34 and an uplink subframe 36. As described previously,during the downlink subframe 34, BS1 transmits to the subscriberstations in the corresponding cell and during the uplink subframe 36 thesubscriber stations transmit to BS1. The wireless receiver within BS1 isactivated during the uplink subframe 36 to receive the transmissions ofthe subscriber stations in the cell.

The second frame 32 also includes a downlink subframe 38 and an uplinksubframe 40. As shown in FIG. 2, there is an overlap 42 between thedownlink subframe 38 associated with BS2 and the uplink subframe 36associated with BS1. Therefore, a portion of the downlink subframe 38may be received by the wireless receiver of BS1 while it is alsoreceiving signals from the subscriber stations. This portion of thedownlink subframe 38 will therefore act as noise/interference in BS1which may compromise the accurate reception of the subscriber signals.To overcome this situation, the first and second base stations may besynchronized so that the downlink subframes 34, 38 and the uplinksubframes 36, 40 align with one another in time. The present inventionrelates to methods and structures for achieving base stationsynchronization in a BWA system.

In one aspect of the present invention, the downlink transmissions ofinterfering base stations are used to provide synchronization for a basestation of interest (BSOI) in a BWA system. FIG. 3 is a flowchartillustrating an example procedure 50 for initiating and maintainingsynchronization between a base station of interest (BSOI) and other basestations in a system in accordance with an embodiment of the presentinvention. The procedure 50 is divided into various phases that arefollowed by the BSOI. In a first phase, known as the discovery phase 52,the BSOI discovers interfering base stations in a surroundingenvironment. As used herein, an “interfering base station” is a basestation whose transmissions are detectable by a BSOI or satisfy somepredetermined interference related criterion (e.g., exceed apredetermined interference receive strength within the BSOI and receivedsignal strength of base station is enough to perform accurate initialand periodic synchronization, etc.). Information is collected for theinterfering base stations for use in selecting a master base station forthe BSOI. Once a master base station has been selected, an initialsynchronization phase 54 may be entered during which the BSOIsynchronizes to the master base station. The BSOI may operate in asubscriber station emulation mode during both the discovery phase 52 andthe initial synchronization phase 54.

After initial synchronization, the BSOI may periodically enter asynchronization maintenance mode 56 during which the BSOI will refreshor correct its synchronization with the selected master base station.This may be done using, for example, a ranging code transmitted by themaster base station at an appropriate time. Every now and then, a“resynchronization mode” 58 may be entered during which the selectedmaster base station and/or other synchronization parameters may bemodified for the BSOI. Using the inventive techniques, a situation mayarise where there are multiple “sync groups” in a BWA system. A syncgroup is a group of base stations that are synchronized to one another.Resynchronization may be required for a BSOI when a new base stationenters the BWA system that discovers interfering base stations withinmultiple different sync groups. If the BSOI is in one of these differentsync groups, it may need to have a new master base station assigned.

The inventive synchronization scheme will often lead to a situationwhere multiple master/slave “levels” are established in a BWA system.FIG. 4 is a diagram illustrating an example base station synchronizationhierarchy 60 that may exist within a BWA system in accordance with anembodiment of the present invention. As shown, in a firstsynchronization level (LEVEL1) of the hierarchy 60, a first base station62 acts as a master base station to slave base stations 64 and 66. In asecond level (LEVEL2), base station 64 acts as a master base station toslave base stations 68 and 70 and base station 66 acts as a master basestation to slave base stations 72 and 74. Any number of different levelsmay be present. The synchronization hierarchy 60 may represent only onesync group within a BWA system. That is, one or more additional syncgroups may also be present. As used herein, the phrase “primary masterbase station” will be used to denote the master base station at thehighest level of the synchronization hierarchy in a sync group.

FIG. 5 is a flowchart illustrating an example method 80 that may be usedby a BSOI during a synchronization discovery phase in accordance with anembodiment of the present invention. It is assumed that the BSOI is tobe activated in a region where a BWA system, having other active basestations, is already established. The BSOI first starts up in subscriberstation emulation mode which allows it to operate as a subscriberstation in the BWA system (block 82). The BSOI then scans thesurrounding environment for interfering base stations in a specifiedfrequency channel and creates a list of interfering base stations (block84). In a system following the IEEE 802.16 standard, each of the basestations in a BWA system will transmit downlink subframes havingpreambles that are encoded with a unique code sequence (e.g. OFDMpreamble or direct sequence spread spectrum). Thus, the BSOI will beable to detect and distinguish the various interfering base stations inthe surrounding environment even though they are all transmittingsubstantially simultaneously on the same frequency channel. Adaptiveantenna system (AAS) techniques may also be employed to avoidinterference between base stations and to establish connections withother base stations. The BSOI may also collect other information on theinterfering base stations that may be used in selecting a master basestation for the BSOI (block 86). The collected information may include,for example, identifiers (IDs) for the detected interfering basestations, received signal level measurements for the interfering basestations, time/frequency/phase offset and propagation delay measurementsfor the interfering base stations, and/or other information. After (orwhile) the information has been (is being) collected, the BSOI may beginto send the information to network control functionality (e.g., BSC 26of FIG. 1) along with a request for the assignment of a master basestation (block 88). The network control functionality may then analyzethe information and select a master base station for the BSOI. Theinformation may be delivered to the network control functionality via awired or wireless link (e.g., IP network 24 of FIG. 1, etc.).

FIG. 6 is a flowchart illustrating an example method 90 for use bynetwork control functionality in a BWA system when a BSOI requests theassignment of a master base station for synchronization purposes inaccordance with an embodiment of the present invention. An interferingbase station list and corresponding collected information, along with amaster base station assignment request, may first be received from theBSOI, as described previously (block 92). It is next determined whetherall of the base stations in the list are within the same sync group(block 94). As described previously, a sync group is a group of basestations that are already synchronized to one another. If the listedbase stations are not all members of the same sync group, a master groupmay be selected from the various groups represented on the list (block96). A predetermined selection criterion may be used to select themaster group from the various groups represented (e.g., select the grouphaving the most members, etc.). If the listed base stations are allmembers of the same sync group, than this sync group automaticallybecomes the master sync group (block 94-Yes).

It may next be determined whether there is at least one master basestation in the master sync group that is also present on the list ofinterfering base stations and that has a receive signal level that isadequate to perform accurate synchronization (block 98). If so, then oneof these master base stations may be selected as the master base stationof the BSOI (block 98-Yes). The ID of this master base station is thendelivered to the BSOI along with a “ranging rule” of the master basestation (block 100). The ranging rule of the master base stationindicates when the master will transmit a ranging code to the BSOI foruse during synchronization maintenance mode to correct thesynchronization between the BSOI and the master. As will be described ingreater detail, each level of a multi-level synchronization hierarchy ina sync group may utilize a different ranging rule from the other levels.

If multiple master base stations in the master sync group are present inthe interfering base station list and have adequate receive signal levelin block 98, then some predetermined criterion may be used to select oneof the master base stations to act as the master base station of theBSOI. For example, in one approach, the master base station having thehighest hierarchical level in the master sync group will be selected tobe the master base station of the BSOI. Using this approach, forexample, the primary master base station in the master group would beselected before a lower level base station. In another selectionapproach, the master base station having the highest received signallevel may be selected, regardless of hierarchical level. A combinationof hierarchical level and signal level may also be used. For example, ifmultiple master base stations are present on a particular hierarchicallevel, and this level is the highest level that includes a master basestation that is also on the list, then the master base station havingthe highest received signal level may be selected. Other selectioncriteria may alternatively be used.

If a master base station of the master sync group having an adequatereceive signal level to perform accurate synchronization is not presenton the list (block 98-No), then another base station from the mastersync group may be selected from the list for use as the master basestation of the BSOI (block 102). A selection criterion may be specifiedfor selecting the base station to serve as the master base station ofthe BSOI (e.g., highest hierarchical level, highest receive signalstrength, etc.). A new ranging rule is then created for the new masterbase station (block 104). The ID of the selected master base station andthe new ranging rule are then delivered to the BSOI and the new master(block 106). The new master may then prepare itself to transmit aranging code at a time dictated by the ranging rule.

It may next be determined whether any groups in the BWA system need tobe resynchronized (block 108). If multiple sync groups are representedon the interfering base station list, and one of the groups was selectedas the master group as described above, then the base stations in theother groups will need to be resynchronized (block 108-Yes). In such acase, the BSOI may be selected as the master base station of the basestations in the other groups (block 110). For each of the other groups,a synchronization chain is developed from the BSOI (block 112). Inaddition, a new ranging rule may be developed for each new master/slavelevel in the synchronization hierarchy (block 114). After this isperformed, the corresponding information (i.e., master base stationassignments and ranging rules) may be delivered to the appropriate basestations in the BWA system (block 116). The method 90 then waits for anext master base station assignment request (block 118). In block 108,if there are no sync groups to be resynchronized (block 108-No), thenthe method 90 may proceed directly to block 118.

Reference back to FIG. 1 is now made to illustrate the operation of themethod 90 of FIG. 6. Assume that base station 16 is to be activate inthe system 10. Before base station 16 is activated, assume there are twosync groups: sync group 1 having base stations 12 and 14 and sync group2 having base stations 18, 20, and 22. Base station 16 collectsinformation on interfering base stations 12, 14, and 18 and sends theinformation, along with a request for a master base station, to BSC 26.BSC 26 determines that the listed base stations are not all in the samegroup. BSC 26 may then select sync group 2, for example, as the mastergroup. Assume base station 18 is the sole master base station in syncgroup 2 and that the received signal strength of the base station 18 isenough to perform accurate synchronization. Because base station 18 ison the list of interfering base stations, it is selected as the masterbase station of base station 16 (i.e., the BSOI). The assigned masterbase station ID and corresponding ranging rule are then delivered tobase station 16.

Because two sync groups were involved and one was selected as the mastergroup, the base stations in the other group (i.e., sync group 1) need tobe resynchronized. Base station 16 is assigned as a master base stationover the base stations in sync group 1. Because both base station insync group 1 (i.e., base station 12 and 14) are on the list ofinterfering base stations for base station 16, they can both becomedirect slaves of base station 16. A new ranging rule is then created forthe new master/slave level. The assigned master base station ID and newranging rule are then delivered to base stations 12 and 14.

FIG. 7 is a flowchart illustrating an example method 120 for use by aBSOI to initially synchronize to a master base station and toperiodically correct this synchronization in accordance with anembodiment of the present invention. The BSOI may first receive the IDof an assigned master base station and the corresponding ranging rule(block 122). The BSOI may then switch to a subscriber station emulationmode if it is not already in such a mode (block 124). While insubscriber station emulation mode, the BSOI may establishsynchronization with the master base station and perform an initialranging procedure (block 126). This may be done in a manner normallyused by subscriber stations in the BWA system to synchronize to anassociated base station (e.g., the manner outlined in the IEEE 802.16standard, etc.). After initial synchronization, the BSOI may switch backto base station mode (block 128).

The ranging rule to be followed by the BSOI will typically specify theframe number in which the assigned master base station will transmit aranging code, as well as the position of the time slot within that framewithin which the ranging code will be transmitted. As described ingreater detail below, in at least one embodiment of the invention, theBSOI will track this ranging rule and allocate a ranging time slotwithin which to receive the corresponding ranging code at periodicintervals. As shown in FIG. 7, the BSOI may first clear a frame counterthat will keep track of the current frame being processed (block 130).The current value of the frame counter may then be checked to determinewhether the appropriate frame number (N) has been reached for theranging rule (block 132). If the frame number has not been reached(block 132-No), the BSOI may then immediately transmit its downlinksubframe and receive its uplink subframe for the current frame (block136). If the frame number has been reached (block 132-Yes), the BSOIwill first allocate a ranging time slot in the current frame withinwhich the ranging code may be received (block 134) before proceeding toblock 136.

If the frame number specified by the ranging rule has been reached bythe frame counter (block 138-Yes), the BSOI will now look for the masterbase station ranging code within the allocated ranging time slot (block142). When detected, the ranging code may be used to estimate frequencyand time offsets for the BSOI (block 144). The frequency and timeoffsets may then be used to adjust a clock of the BSOI to synchronizethe BSOI with the master base station (block 146). The method 120 maythen proceed back to block 130 where the frame counter is once againcleared. If the frame number specified by the ranging rule has not beenreached by the frame counter (block 138-No), the frame counter will beincremented by 1 (block 140) and the method 120 will return to block 132(i.e., no ranging code will be received during the current frame). Theprocess will then repeat until the frame counter reaches the appropriateframe number. In this manner, the synchronization of the BSOI to themaster base station may be periodically corrected or refreshed.

FIG. 8 is a timing diagram illustrating example communication activity150 within a sync group of BWA system in accordance with an embodimentof the present invention. As shown, the sync group includes four basestations (BS1, BS2, BS3, BS4) that each communicate with correspondingsubscriber stations using frames in a common frequency channel. Each ofthe frames is divided into a downlink subframe 152 and an uplinksubframe 154. At the beginning of each downlink subframe 152, thecorresponding base station transmits a preamble 156 that may be used byassociated subscriber stations to synchronize to the base station. Thecommunication activity 150 represents a multi-level master/slavehierarchy. That is, BS1 acts as a master to slave BS2 within a firstlevel of the hierarchy and BS2 acts as a master to slaves BS3 and BS4within a second level of the hierarchy. The ranging rule for the firstlevel of the hierarchy indicates that a ranging code 160 may betransmitted by the master (BS1) in frame 1 (158) of the frame sequence,in the last time slot of the frame. Thus, slave BS2 allocates a rangingtime slot 162 within which to receive the ranging code 160. Likewise,the ranging rule for the second level of the hierarchy indicates that aranging code 164 may be transmitted by the master (BS2) in frame 2 (166)of the frame sequence, in the last time slot of the frame. Thus, slavesBS3 and BS4 allocate ranging time slots 168 and 170 within which toreceive the ranging code 164. The slave base stations BS2, BS3, BS4 mayuse the received ranging codes to estimate frequency and time offsetsfor use in refreshing synchronization to corresponding master basestations. Although not shown in FIG. 8, the frame sequences (i.e., frame1, frame 2, etc.) will eventually repeat in time for each base station.

FIG. 9 is a block diagram illustrating an example BSC architecture 180in accordance with an embodiment of the present invention. The BSC 180may be used, for example, within the BWA system 10 of FIG. 1 or in otherBWA systems. As shown, the BSC 180 may include: a transceiver 182, acontroller 184, and a sync group database 186. The transceiver 182 isoperative for receiving signals from and sending signals to basestations in the BWA system. A receiver portion of the transceiver 182may receive, for example, a list of interfering base stations andrelated information as well as a request for assignment of a master basestation from a BSOI. When a master base station assignment has been madefor the BSOI, a transmitter portion of the transceiver 182 may transmitthe assignment information to the BSOI.

The controller 184 may make the actual master base station assignmentdecisions. In at least one embodiment, the controller 184 may beconfigured during system operation to perform the method of FIG. 6 orvariations thereof. The controller 184 may be implemented within one ormore digital processing devices within BSC 180. The digital processingdevice(s) may include, for example, a general purpose microprocessor, adigital signal processor (ASP), a reduced instruction set computer(RISC), a complex instruction set computer (CISC), a field programmablegate array (FPGA), an application specific integrated circuit (ASIC),and/or others, including combinations of the above.

The sync group database 186 may be used by the controller 184 to storeinformation about the sync groups that are currently present within theBWA system. This may include information on the members of each syncgroup, the synchronization hierarchies of each sync group, the rangingrules used at each master/slave level of a sync group, signal strengthof interfering base stations at the location of each base station,propagation loss between base stations, and/or other sync group relatedinformation. The controller 184 may consult the sync group database 186during the master base station assignment process for a BSOI. After adecision has been made by the controller 184, appropriate modificationmay be made to the sync group database 186 to reflect the decision. Anyresynchronizations performed by the controller 184 will also be recordedwithin the sync group database 186.

In at least one embodiment of the present invention, low-cost basestations are provided for use in a BWA system that do not include GPSreceivers. That is, features of the invention are utilized to providesynchronization between base stations within the system, thuseliminating the need for GPS receivers in the base stations. In someother embodiments, the inventive features are made available in additionto GPS receiver technology within a base station to provide analternative synchronization means for use in, for example, indoorenvironments and in other scenarios where an adequate number of GPSsatellites may not be acquired.

In the foregoing description, terminology has been used that is oftenassociated with the IEEE 802.16 wireless networking standard. It shouldbe appreciated, however, that the invention is not limited to use withinIEEE 802.16 related systems. That is, the base station synchronizationtechniques described herein may have application in a wide range ofdifferent cellular based wireless systems. In addition, the inventiveprinciples are not limited to use within systems utilizing OFDM or OFDMAcommunication techniques.

The techniques and structures of the present invention may beimplemented in any of a variety of different forms. For example,features of the invention may be embodied within laptop, palmtop,desktop, and tablet computers having wireless capability; wireless basestations; wireless access points; base station controllers; networkinterface cards (NICs) and other network interface structures;integrated circuits; as instructions and/or data structures stored onmachine readable media, and/or in other formats. Examples of differenttypes of machine readable media that may be used include floppydiskettes, hard disks, optical disks, compact disc read only memories(CD-ROMs), digital video disks (DVD), Blu-ray disks, magneto-opticaldisks, read only memories (ROMs), random access memories (RAMs),erasable programmable ROMs (EPROMs), electrically erasable programmableROMs (EPROMs), magnetic or optical cards, flash memory, and/or othertypes of media suitable for storing electronic instructions or data.

In the foregoing detailed description, various features of the inventionare grouped together in one or more individual embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed inventionrequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects may lie in less thanall features of each disclosed embodiment.

Although the present invention has been described in conjunction withcertain embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art readily understand.Such modifications and variations are considered to be within thepurview and scope of the invention and the appended claims.

1. A computer implemented method comprising: acquiring information aboutinterfering base stations in a vicinity of a base station of interest(BSOI); and choosing one of said interfering base stations as a masterbase station for said BSOI, wherein a master base station is a basestation to which another base station is to synchronize; whereinchoosing one of said interfering base stations as a master base stationincludes: when said interfering base stations are from multiple syncgroups, selecting a sync group from said multiple sync groups to be amaster sync group, wherein a sync group is a group of base stations thatare currently synchronized with one another; when said interfering basestations are all from a common sync group, identifying said common syncgroup as said master sync group; and when said master sync groupincludes at least one master base station that is also one of saidinterfering base stations and that has a received signal strength withinsaid BSOI that is adequate to perform accurate synchronization,assigning one of said at least one master base station as a master basestation of said BSOI.
 2. The method of claim 1, further comprising:delivering an ID of said assigned master base station and acorresponding ranging rule to said BSOI.
 3. The method of claim 1,wherein choosing one of said interfering base stations as a master basestation further includes: when said master sync group does not include amaster base station that is also one of said interfering base stationsand that has a received signal strength within said BSOI that isadequate to perform accurate synchronization, selecting a base stationfrom said master sync group that is one of said interfering basestations as the master base station of said BSOI; and creating a newranging rule for said selected master base station.
 4. The method ofclaim 3, further comprising: delivering an ID of said selected masterbase station and said new ranging rule to said BSOI and said selectedmaster base station.
 5. The method of claim 1, further comprising: whensaid interfering base stations are from multiple sync groups and one ofsaid multiple sync groups has been selected as said master sync group,giving said BSOI master status over sync groups in said multiple syncgroups other than said master sync group.
 6. The method of claim 5,further comprising: identifying synchronization chains for said syncgroups in said multiple sync groups other than said master sync group,wherein each synchronization chain originates at said BSOI; and creatinga new ranging rule for each master/slave level within eachsynchronization chain.
 7. The method of claim 1, wherein: acquiringinformation includes receiving said information from said BSOI, whereinsaid information is accompanied by a request to assign a master basestation to said BSOI.
 8. A base station controller (BSC) comprising: areceiver to receive a list of interfering base stations associated witha base station of interest (BSOI); a controller to select a master basestation for said BSOI from said list of interfering base stations,wherein a master base station is a base station to which another basestation is to synchronize; and a sync group database to store datarelated to base station sync groups in an associated wireless network,each sync group including one or more base stations in said wirelessnetwork that are currently synchronized to one another, wherein saidcontroller is in communication with said sync group database; whereinsaid controller is to: (a) when said base stations in said list ofinterfering base stations are from multiple sync groups, select a mastersync group from said multiple sync groups; (b) when said base stationsin said list of interfering base stations are from a common sync group,identify said common sync group as said master sync group; and (c)select a base station from said list of interfering base stations, thatis within said master sync group, for use as a master base station forsaid BSOI.
 9. The BSC of claim 8, wherein: operation to select a basestation from said list includes operation to: when said master syncgroup includes at least one master base station that is also one of saidinterfering base stations and that has a received signal strength insaid BSOI that is adequate to perform accurate synchronization, assignone of said at least one master base stations as a master base stationof said BSOI.
 10. The BSC of claim 9, wherein: operation to select abase station from said list includes operation to: when said master syncgroup does not include a master base station that is also one of saidinterfering base stations and that has a receive signal strength withinsaid BSOI that is adequate to perform accurate synchronization, select abase station from said master sync group that is one of said interferingbase stations as the master base station of said BSOI.
 11. The BSC ofclaim 10, wherein: operation to select a base station from said listincludes operation to: when said master sync group does not include amaster base station that is also one of said interfering base stations,create a new ranging rule for said selected master base station.
 12. TheBSC of claim 8, wherein said controller is configured to: when said basestations in said list of interfering base stations are from multiplesync groups and one of said sync groups has been selected as a mastersync group: give said BSOI master base station status over sync groupsin said multiple sync groups other than said master sync group; identifysynchronization chains for said sync groups in said multiple sync groupsother than said master sync group, wherein each synchronization chainoriginates at said BSOI; and create a new ranging rule for eachmaster/slave level within each synchronization chain.
 13. The BSC ofclaim 8, further comprising: a transmitter to transmit a master basestation ID and a corresponding ranging rule to said BSOI.
 14. An articlecomprising a machine readable storage medium having instructions storedthereon that, when executed by a computing platform, operate to: acquireinformation about interfering base stations in a vicinity of a basestation of interest (BSOI); and choose one of said interfering basestations as a master base station for said BSOI, wherein a master basestation is a base station to which another base station is tosynchronize; wherein operation to choose one of said interfering basestations as a master base station includes operation to: when saidinterfering base stations are from multiple sync groups, select a syncgroup from said multiple sync groups to be a master sync group, whereina sync group is a group of base stations that are currently synchronizedwith one another; when said interfering base stations are all from acommon sync group, identify said common sync group as said master syncgroup; and when said master sync group includes at least one master basestation that is also one of said interfering base stations and that hasa received signal strength within said BSOI that is adequate to performaccurate synchronization, assign one of said at least one master basestations as a master base station of said BSOI.
 15. The article of claim14, wherein: operation to choose one of said interfering base stationsas a master base station further includes operation to: when said mastersync group does not include a master base station that is also one ofsaid interfering base stations and that has a received signal strengthwithin said BSOI that is adequate to perform accurate synchronization,select a base station from said master sync group that is one of saidinterfering base stations as the master base station of said BSOI; andcreate a new ranging rule for said selected master base station.
 16. Thearticle of claim 14, wherein: operation to choose one of saidinterfering base stations as a master base station further includesoperation to: when said master sync group does not include a master basestation that is also one of said interfering base stations and that hasa received signal strength within said BSOI that is adequate to performaccurate synchronization, select a base station from said master syncgroup that is one of said interfering base stations as the master basestation of said BSOI; and create a new ranging rule for said selectedmaster base station.
 17. The article of claim 16, wherein saidinstructions further operate to: deliver an ID of said selected masterbase station and said new ranging rule to said BSOI and said selectedmaster base station.
 18. The article of claim 14, wherein saidinstructions further operate to: when said interfering base stations arefrom multiple sync groups and one of said multiple sync groups has beenselected as said master sync group, give said BSOI master status oversync groups in said multiple sync groups other than said master syncgroup.
 19. The article of claim 18, wherein said instructions furtheroperate to: identify synchronization chains for said sync groups in saidmultiple sync groups other than said master sync group, wherein eachsynchronization chain originates at said BSOI; and create a new rangingrule for each master/slave level within each synchronization chain.